The present invention relates generally to an air induction system for a vehicle engine and more particularly to flow turning vanes and hydrocarbon adsorbents included in the air induction system.
Motor vehicle manufacturers are continually trying to obtain greater power output from given size engines, even while meeting new environmental emissions and fuel economy requirements. One area of the overall engine system that is being closely scrutinized is the air induction system. This area is being scrutinized because one factor relating to the maximum engine power output is the air flow capacity through the air induction system—the lower the air flow capacity the lower the maximum engine power output. Consequently, the pressure loss of the air induction system must be minimized to provide a desired amount of air flow for maximizing engine power output. However, the emissions and fuel economy requirements are creating the undesired effect of causing more flow restrictions.
An emissions requirement that may have an adverse effect on airflow capacity is a requirement to reduce evaporative hydrocarbon emissions from vehicles. In response to this requirement, hydrocarbon adsorbents have been added in air cleaner housings. The adsorbents reduce hydrocarbon emissions caused by vapors escaping from the air induction system after engine shutdown. That is, when the engine is shut down, residual unburned fuel inside the cylinder head and intake runner evaporates to form hydrocarbon vapor, which flows through the engine throttle body and into the air induction system. Then, hydrocarbons, if not trapped, can leak out into the atmosphere through the air induction system. The hydrocarbon adsorbent traps the hydrocarbon vapor.
There are generally two types of hydrocarbon trapping devices in use—flow-through adsorbents and non-flow-through adsorbents. The non-flow-through adsorbent may include a carbon liner or carbon bag mounted on an internal wall of the air cleaner housing, so the air does not flow through it. A concern with this type of trapping device is that it may have a relatively low adsorbing efficiency, with only a small amount of hydrocarbon molecules being trapped relative to the size of the trap. The flow-through adsorbent, on the other hand, may include a honeycomb carbon adsorbent that is mounted across the duct air passage, or a panel carbon adsorbent that is mounted in the air cleaner housing parallel with the air filter. While this type of hydrocarbon adsorbent generally has higher adsorbing efficiency, it creates a restriction in the air flow path, thereby causing pressure loss. To reduce the pressure losses, the flow-through types may be designed with a large percentage of open area across their faces. But this, then, results in the low adsorbing efficiency that was inherent in the non-flow-through types.
The other type of vehicle requirement—fuel economy—may also lead to air flow restrictions, although indirectly so. To improve fuel economy, vehicles, and especially engine compartments, have been reduced in size. This reduction in size often leads to packaging compromises that require the shape of the air induction system components to be less than ideal for maximum air flow. For example, the inlet air is typically drawn in from a front corner behind a headlamp of the vehicle, where the air is cool and at a relatively high pressure. After passing through the air cleaner, where it is filtered, it is drawn into a clean air duct. The clean air duct typically must turn about 90 degrees—with a sharp radius and short length—to direct flow to a throttle body. The 90-degree bend of the clean air duct causes significant flow recirculation and stagnant flow near the inside of the bend, with a resulting air flow pressure loss in this duct. The air flow pressure loss can lead to a reduction in the maximum engine power output.
In order to overcome this pressure loss, some have located turning vanes at the bend in the clean air duct. Turning vanes, in effect, divide the duct into multiple ducts that have closer to ideal bend radii to duct diameter ratios, and they provide a surface that forces air in the flow stream around the bend. Consequently, a duct having turning vanes in its bend almost fully uses the duct cross section, greatly reducing the pressure drop across the bend. The turning vanes may also help to reduce entrance losses into the throttle body and distribute air equally to all cylinders, with a resulting improved flow performance. Thus, a greater air flow through the air induction system may allow for greater maximum engine power output.
But turning vanes are not commonly used in air induction system because they are typically not cost effective if used only for reducing the pressure loss. In many cases, engineers cannot justify the benefits of turning vanes compared to the cost associated with adding the vanes. So instead, engineers struggle with increasing bend ratios (bend radius/duct diameter) as much as possible. However, due to packaging constraints in the vehicle engine compartment, engineers often come up short of the desired bend ratio and live with the pressure loss caused by the sharp bend in the clean air duct.